Scottish unionists have been branded "a disgrace" by the SNP for insisting that independence will be "the death knell" of shipbuilding in Scotland.

Labour leader Johann Lamont was called "a disgrace to Scotland" by an SNP MSP during a rowdy Labour-led debate at Holyrood.

An SNP minister also described Scottish Secretary Alistair Carmichael's promotion of Portsmouth's shipbuilding capability as "a disgrace".

Labour MP for Govan Ian Davidson, convener of Westminster's Scottish Affairs Committee, was accused of threatening workers with their jobs if they vote for independence.

Labour hit back with a roll call of senior shipyard workers who have voiced fears about independence and demanded that the SNP withdraw their comments.

Scotstoun union conveners John Dolan and Duncan McPhee, Rosyth trade unionists Raymond Duguid and Eric McLeod and former Confederation of Shipbuilding Unions general secretary John Wall have all raised concerns about independence in recent weeks, according to Ms Lamont.

She said: "No matter how inconvenient it is for some people, there is only one game in town.

"The only option for bridging the gap between the carrier project that kept Govan and Scotstoun open and any future plans for shipbuilding is naval contracts.

"There is now only one barrier to Scottish shipbuilding and that is the referendum on Scottish independence. If Scotland votes yes next year, it will be the death knell of a proud industry."

Her comments were met with jeers from the SNP and the party's MSP for Clydebank Gil Paterson was called to order amid shouts of "you're a disgrace to Scotland" in Ms Lamont's direction.

Earlier, Mr Paterson said Mr Davidson had "threatened Govan workers if they exercise their democratic right to vote, perhaps for independence or not, that they would lose their jobs".

Ms Lamont said: "Ian Davidson stands second to none in championing the interests of shipyard workers. He has fought to secure jobs in the face of the threat placed on them by the SNP's commitment to separate Scotland from the rest of the UK."

Labour MSP Neil Findlay suggested it was out of order "for a member to shout 'you are a disgrace to Scotland' to a member who is defending her constituency interests" and invited the MSP "to withdraw that disgraceful comment".

Scottish Government transport minister Keith Brown also attacked Mr Davidson for reportedly suggesting new Ministry of Defence shipbuilding contracts could come with "a break clause" if Scotland votes for independence.

Mr Brown said: "The approach of the No campaign appears to be 'anywhere but Scotland'.

"Ian Davidson has dreamed up and advocates a break clause to deny the yards in his own constituency the Type 26 contracts should Scotland vote for independence.

"In the words of Alistair Carmichael: 'If Scotland were to vote yes you would think that Portsmouth would be well placed in that circumstance'.

"You have the Secretary of State for Scotland promoting Portsmouth as the place that should get the Type 26 contracts.

"His job is meant to promote Scotland in the Cabinet, not promote the Cabinet in Scotland. He should defend these Scottish jobs and it's a disgrace that he hasn't done so."

Tories and the Liberal Democrats echoed Labour's claims that a Yes vote in the referendum would lead to job losses for the shipyards on the Clyde.

Conservative Murdo Fraser said work at the yards, and other defence companies in Scotland, was "underpinned by UK domestic contracts from the Ministry of Defence".

He argued: "The key issue in this debate is what happens in the event of a Yes vote in the referendum.

"And the simple fact here is no UK government since the Second World War has ever had a complex warship built in any foreign country. And post the referendum, if Scotland votes Yes, Scotland will be a foreign country."

He said the contract for Type 26 frigates, which is set to go to Glasgow at the moment, would not be signed till after the referendum next September.

"It's the UK Government that will make the final decision as to where these contracts are placed," Mr Fraser said.

"Why would the UK Government break with convention and place these contracts anywhere outwith their own home country?"

He insisted: "Despite the protestations from the SNP benches, it is absolutely clear the future of Govan is threatened by independence. Those jobs are under threat if people vote Yes in the referendum in September next year."

Liberal Democrat leader Willie Rennie told MSPs the yard in Portsmouth would not be closed till after the independence referendum.

"It's no coincidence that is the case," he said.

"The order for the Type 26 frigates will not be placed till after the referendum. The UK Government are defending our own defence interests. That is the reality."

SNP MSP Annabel Ewing argued the contract for the frigates could still come for the Clyde, even if Scotland voted to leave the UK.

"The ships will be built where it makes the most sense to do so," she said.

"That is the key political message coming from the UK Secretary of State for Defence, the Chief of the Defence Staff, and that is the only conclusion that makes any commercial sense."

With shipbuilding at Portsmouth due to end next year, Ms Ewing added: "It is the case that the Clyde will be the only place now on these isles with the capacity to build large complex warships."

She went on: "It's a no-brainer. It's quite clear from an examination of the facts that naval procurement in Scotland will continue and with respect to the Type 26 ships these will indeed be built on the Clyde."